POLYMERS
What is a polymer?
• Polymers are large molecules made up small repeating units.
• The repeating units in a polymer are called monomers.
• Monomers are linked together in a polymerization reaction.
• Polymers are widely abundant and may be natural or synthetic.
• Some examples of polymers are rubber, polyvinyl chloride (PVC), polyethylene, Teflon, Kevlar, carbohydrates, proteins
Addition Polymers
• Addition polymers result from addition reactions of monomers containing carbon-carbon double bonds.
• Some examples of addition polymers include polyethene, polypropene, polyvinyl chloride, polystyrene and Teflon
C C C C C C+ + C C C C C C
ethene etheneethenepolyethene or polyethylene
C C
n
OR
Example
Stages in an Addition Polymerization Reaction
• There are 3 stages in an addition polymerization reaction.
• Initiation an initiating molecule (such as a peroxide) with an unpaired electron forms a bond with one of the C’s in the double bond.
• Propagation the “growing” phase.• Termination the unpaired electron ends combine
forming a covalent bond ending the reaction.
Condensation Polymers
• Condensation polymers are formed when monomers are linked together through condensation reactions (removal of water).
• Examples of condensation polymers include polyester, proteins, carbohydrates and Kevlar
Example
O
CH2OH
OH
OH
OH
OHH
H
HH
H
galactose
O
CH2OH
O
OH
OH
OH
H
H
H
HH
glucose
H
O
CH2OH
OH
OH
OH
H
H
HH
H
O
CH2OH
OOH
OH
OH
H
H
H
HH
+ H2O
lactose
Types of condensation polymer linkages
a) Ester linkages (you have seen these in esterification reactions)
(a reaction between a carboxylic group and an alcohol (hydroxyl group))
- polymers with ester linkages have the general name of polyesters
Eg. Polyethylene, PET
Types of condensation polymer linkages
b) Amide linkages
- Occur between an amine group and a carboxyl group
- Called polyamides in general
- Examples include Kevlar, Dacron
The Effect of Substituted Groups on Polymer Properties
• The reactivity, solubility and strength of a polymer is due to the groups that are attached to the polymer chain.
• Teflon (polytetrafluoroethane) for example is very unreactive because the C-F is very strong.
• Monomers that contain 2 double bonds are able to add to other molecules in two ways which means a single monomer can be incorporated into 2 different polymer chains causing bridges between the polymer chains.
• These bridges are called “crosslinks” and may be formed intermittently along the polymer chains.
• These links between polymer chains are covalent bonds and are much stronger than the van Der Waals forces that would otherwise hold the chains together.
• As the degree of crosslinking increases so does the strength of the molecule.
• A high degree of crosslinking will also make the polymers heat resistant and more elastic.
• Crosslinks may also be formed with inorganic crosslinking agents such as sulfur.
Homework
Page 121
#53-#62
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